1. Field of the Invention
The present invention relates to a buttonhole presser device that is attached to a zigzag sewing machine and used when stitching a buttonhole. In particular, the present invention relates to a buttonhole presser device that is capable of measuring the diameter of a button and stitching a buttonhole having a length corresponding to the measured diameter of the button and a method of stitching a buttonhole by using the buttonhole presser device.
2. Description of the Related Art
As illustrated in FIGS. 6A to 6E, in order to stitch a buttonhole by using a zigzag sewing machine, it is necessary to draw a buttonhole mark Mc at a position on a piece of fabric where a buttonhole is to be stitched, lift a presser foot and place the piece of fabric between the presser foot and a needle plate so that a needle passes through a start point Ms of the buttonhole mark Mc, stitch left and right line tacks and upper and lower bar tacks as illustrated in FIG. 6E, and switch the fabric feed direction in accordance with the length of the buttonhole mark Mc between the start point Ms and the end point Me. However, it is necessary for a user to pay careful attention in order to set the length of a buttonhole in accordance with the size of a button and switch the fabric feed direction at the start point or the end point of the buttonhole. Therefore, stitching a buttonhole is cumbersome for a user.
To solve the problem, buttonhole presser devices of zigzag sewing machines having the following structures have been developed (see, for example, Japanese Examined Patent Application Publication No. 62-40035 (U.S. Pat. No. 4,181,087), and Japanese Unexamined Patent Application Publication No. 5-309186). Each of the buttonhole presser devices includes a fabric feed frame unit that is slidably attached to a fabric presser. The fabric feed frame unit has a frame in which an elongated hole, for allowing a buttonhole to be stitched, is formed. The buttonhole presser device includes a button-diameter measuring unit for measuring the diameter of a button. The buttonhole presser further includes switching means for automatically switching the fabric feed direction by setting the length of a buttonhole corresponding to the diameter of a button gripped by the button-diameter measuring unit.
However, the button-diameter measuring units of the buttonhole presser devices described in Japanese Examined Patent Application Publication No. 62-40035 and Japanese Unexamined Patent Application Publication No. 5-309186 have the following problems. First, members of the presser devices for gripping a button therebetween are designed for gripping a circular button. Second, the members are capable of holding a button having a diameter smaller than about 25 mm, and it is not possible to stitch a buttonhole for a button having a larger size.
In recent years, ornamental buttons having a diameter greater than 25 mm are widely used, and therefore an increasing number of users want to stitch buttonholes for large buttons. Moreover, large buttons that are not circular but elliptical, polygonal (such as pentagonal), flower-shaped, or in the shapes of cartoon characters are being increasingly used.
It may be possible to stitch a buttonhole for a large button having a diameter greater than 25 mm by increasing the size of button-diameter measuring means of an existing buttonhole presser device. However, by only doing so, it may not be possible to stitch buttonholes for large buttons having noncircular irregular shapes. When attaching a noncircular button to a garment, it is important to attach the button in the correct orientation and it is necessary to change the length of the buttonhole in accordance with the orientation of the button. However, existing button-diameter measuring means has a problem in that, because the button may naturally rotate relative to a member for gripping the button depending on the orientation of the button, the button might not be gripped in an appropriate orientation and the button may become removed from the button-diameter measuring means.
When the buttonhole presser device is attached to a zigzag sewing machine in a state in which the button-diameter measuring means is gripping a large button having a considerable weight, the buttonhole presser device may become inclined due to the weight of the large button. As a result, a problem arises in that it is difficult to set a piece of fabric in which a buttonhole is to be formed.
Existing button-diameter measuring units perform positioning of a button by using a latch mechanism having a predetermined pitch. Therefore, it is difficult for the button-diameter measuring units to correctly measure the diameter of a button with a precision smaller than the pitch. Furthermore, because the latch mechanism is not securely fixed, the position of the button-diameter measuring unit may be easily displaced due to an accidental impact, and therefore the measured diameter of a button may be changed. As a result, there is a problem in that it is difficult to repeatedly stitch buttonholes having the same size.